1. Field of the Invention
The invention is directed to an air control valve, and in particular, to a carburetor for an internal combustion engine embodying novel air control and vacuum valves controlling the air flow to the engine and providing vacuum signals controlling the operation of one or more accessories.
2. Background of the Invention
Various types of air control valves and carburation means have been used for supplying a controlled quantity of an air/fuel mixture to an internal combustion engine. The most commonly used today embodies a butterfly type valve in the throat of a generally cylindrical passageway for controlling the primary air flow in response to an operator's command. A venturi located upstream of the butterfly valve creates a low pressure region which asperates fuel into the engine's intake manifold. With the advent of electronic fuel control and its attendent fuel injection systems, the need for the venturi section of the present carburetor systems has been eliminated. However, the butterfly valve for controlling the air flow has for the most part survived the transition as a means for controlling the air flow. Probably, the main reasons for the survival of the butterfly valve is its extreme simplicity, ease of manufacture and its characteristics are well known. The disadvantages of the butterfly valve is that the resultant air flow in the immediate vicinity of the valve is unsymmetrical, particularly when the valve angle is small, less than thirty degrees. This unsymmetrical air flow perturbates the air/fuel distribution in the engine's intake manifold. With the present emphasis on emissions control and fuel economy, this perturbation of the air/fuel distribution increases both fuel consumption and the emissions of undesirable exhaust gases.
Another factor which also has become important is the generation of the vacuum signals which operate vacuum motors controlling peripheral accessories of the engine, which also play a part in the emissions and economy of the engine. Of primary importance today are the engine's spark or ignition advance system and the exhaust recirculation valve. For the most efficient operation of the engine, the air flow and, therefore, the setting of the valves control member at which these peripheral devices are actuated, needs to be controlled with a fair degree of precision. Unfortunately, the butterfly valve configuration is not well suited for generating these vacuum signals with the degree of precision desired.
Alternate approaches to the butterfly valve for controlling the air flow to an internal combustion engine have been disclosed in the prior art. Typical examples of these are U.S. Pat. No. 795,273 issued to L. A. Essner (1905) and 1,238,433 issued to B. Pendersen (1917). Both of these patents teach concentric discs, each having one or more mating apertures. Rotating the discs relative to each other increases and decreases the effective aperture formed by the mating apertures. A similar type valve is also shown in U.S. Pat. No. 1,797,293 issued to J. H. McSlvaine for controlling the air flow of a centrifugal fan. Another variation is shown in U.S. Pat. No. 3,934,564 issued to Barnert in 1976, as applied to an exhaust gas recirculation valve.
Disclosed herein is a carburetor embodying an air control valve which overcomes the disadvantages of the butterfly valve and other air control valves of the prior art and is capable of generating the desired vacuum signals.